While overhead door openers have taken a variety of forms, one of the more common types for moderate to heavy service in opening and closing horizontally-sectioned folding vehicle doors employs parallel-rail overhead trackage for a trolley connected by a suitable link or linkage to the upper section of the door, and drawn to and fro on the rails by an essentially endless roller chain trained over a drive sprocket at one end of the track and a return sprocket at the other.
As each run of the chain in such arrangements is somewhat longer than the height of the door, it is apparent that as sprocket size is reduced for overall height reduction in those chain drives whose chain loops lie in a vertical plane, the catenary sag of the upper run of the chain can bring it into contact with the trolley as those members move in opposite directions during operation, particularly in drive chains of door-operators for tall doors. Not only is such contact noisy, but the sliding contact of the chain links with the upper surface of the trolley causes unnecessary wear on both the chain and the trolley, needlessly increasing the expense of maintenance.
It is accordingly an object of this invention to provide a chain guide and support for vertically-oriented chain loops of door-operators which will lift the upper run of the chain out of contact with the oppositely moving trolley, and support the chain by its individual rollers and thus out of chain-link contact with the trolley or other relatively moving parts.